FIG. 1 shows the basic schematic layout of a gas turbine, as is used as a stationary industrial turbine, for example, for generating power. The gas turbine 10 of FIG. 1 comprises a compressor 12 which via an air intake 11 inducts and compresses combustion air. The compressed air is introduced into a combustion chamber 13 and used there for combusting a fuel 14. The ensuing hot gases are expanded in a subsequent turbine 15, performing work, and are discharged to the outside as exhaust gas 16 or put to further use in a heat recovery steam generator.
The rotor blades which are required for the compressor 12 and the turbine 15 are usually attached on a rotor 17 which has corresponding rotor disks. In the compressor 12, during compression of the combustion air, temperatures of more than 100° C. occur at the compressor exit. Cooling of the rotor in this region on the one hand reduces in this case the thermal loading of the materials which are used but on the other hand can also be conducive to altogether improving the efficiency of the gas turbine. For the cooling, some of the compressed air can be tapped off, cooled down in a cooling device 18 (dashed lines in FIG. 1), and can then be fed into the exit region of the compressor 12 for cooling purposes.
In printed publication EP 0 799 971 B1, it has been proposed, for protection of the rotor against a thermal overload in the exit region of the compressor, to provide a thermal barrier which reduces the entry of heat from the compressor passage into the rotor body. In this case, however, it involves a purely passive measure which does not enable dissipation of the heat.
From GB 2 350 408 A, it is also known—in the case of the rotor of a turbomachine—to arrange a concentric annular thermal shield element at a distance around the rotor, which thermal shield element carries the rotor blades and reduces the entry of heat into the rotor. In addition, a cooling medium can flow through a gap between the ring and the rotor, which dissipates heat. In this case, it is disadvantageous that the shield element, for want of separate cooling, makes particular demands upon the material. Furthermore, cooling medium, which flows through beneath the shield elements, can be fed back only into the compressor, as a result of which the compressor discharge temperature rises. Furthermore, this cooling medium is no longer available for the combustion chamber or for turbine cooling.
The present-day design at the exit of the compressor, beyond which the invention extends, according to FIG. 2 comprises compressor blades 21 which are fastened in circumferential grooves 20′ on the rotor 17 or on the rotor disk 25′. In most industrial gas turbines, some of the compressed compressor air is tapped off and instead of being supplied to the combustion is used as cooling air of hot parts (rotor, hot gas parts). In order to improve the efficiency of the cooling, some of the compressor air is sent through a cooler in order to achieve a lower temperature of the cooling medium (see above). In the case of the gas turbine of FIG. 2, some of this precooled cooling air 24 is fed back to the exit of the compressor 12 via (stationary) structural parts 23′ of a center section 19 which adjoins the compressor 12 downstream. The cooling air in this case is used for purging the cavity 22 between the compressor rotor exit and the center section 19 and also as cooling air for the rotor disk 25′ in the region of the compressor rotor exit. It is the aim to lower the rotor temperature in this region with the cooling air.
Although it is the aim to lower the rotor temperature in this region with the cooling air, this type of cooling is not efficiently adequate for the rotor disk 25′. In order to increase the output and therefore the efficiency in a gas turbine, the combustion temperature and/or the mass flow can be increased. An output increase can be achieved by means of an improved compressor. This results in a higher mass flow so that the pressure and therefore the air temperature at the exit of the compressor increase and consequently the rotor temperature also rises. With higher rotor temperature in the region of the compressor rotor exit, however, the service life of the rotor is negatively influenced.